Tillane is a genius. Even if he (er, assuming you're a bloke, apologies if not
) is wrong it's a brilliant idea.
Got to say I considered the season 3 finale somewhere between pants and fungally infested pants. So far this ending is excellent, I can't remember the last time I found a Dr Who story this enthralling (well, actually it was Genesis of the Daleks a few years ago).
I wonder if RTD and Moffat have had a long talk about the implications because, as I said on the Stolen Earth thread, interfering in the 'timelocked' Time War could release the Timelords, including Romana and others, broadening the possibilities.